1. Field of the Invention
The present invention relates generally to an interface circuit and an input buffer integrated circuit including the same. More particularly, the invention relates to an interface circuit which is provided in a peripheral device or so forth inputting an output signal of a personal computer (hereinafter referred to as PC) or the like for controlling an input signal level of an input buffer inputting the output signal of the PC or the like, and an input buffer integrated circuit including the same.
2. Description of the Related Art
FIG. 10 is an illustration showing a construction of the conventional interface performing exchange of data between a PC and a peripheral device. The interface shown in FIG. 10 is constructed with an output buffer 2 on the side of the PC, an input buffer 5 on the side of the peripheral device and a cable 3 connecting both buffers. The output buffer 2 is provided in a buffer integrated circuit 1 integrated into a single chip. On the other hand, the input buffer 5 is provided within a buffer integrated circuit 6 integrated into a single chip.
In such interface, if impedances of an output stage of the output buffer 2 and an input stage of the input buffer are unmatching with each other, reflection is caused in the signal at the input stage of the input buffer 5. Due to reflection, ringing, such as simulation waveform shown in FIG. 11 is caused in the signal of the input stage of the input buffer 5. In FIG. 11, PCOUT corresponds to an output waveform of the output buffer 2 on the side of PC shown in FIG. 10, and PERIN corresponds to an input waveform of the input buffer 5 on the side of the peripheral device, respectively. It should be noted that FIG. 11 shows an operation upon falling down of the signal.
On the other hand, an advanced technology (AT) interface to be frequently used in the interface between the PC and the peripheral device, exchange of data is performed according to transistor transistor logic (TTL) standard. Therefore, if ringing exceeds 0.8V of the waveform in a period (a) in FIG. 11, ringing can be erroneously recognized as "H" level signal to result in malfunction in the input buffer 5 on the side of the peripheral device.
Essentially, ringing due to reflection can be reduced by matching of impedances. However, for the peripheral device, for which connection with unspecified PC, impedance matching is difficult to establish for variation of condition for difference of specification and material of output driver, connection cable, connecting connector and so forth.
Therefore, seeking for impedance matching cannot be effective measure for ringing.